The present invention relates in general to semiconductor power device technology and in particular to trench gate field effect transistors with improved body to gate alignment.
In conventional trench gate field effect transistors (FETs), the alignment of the body region to the bottom of the gate electrode impacts the transistor channel length and thus the on-resistance RDS(on) and gate-drain charge QGD. If the body region extends too deep, RDS(on) goes up and QGD goes down. If the body region is too shallow, QGD goes up and RDS(on) goes down. Unfortunately, this alignment is subject to large variations due to several factors including variations in the doping concentration of both the epitaxial layer and the body region that is formed in the epitaxial layer, the body drive-in process, and the trench recess. In more complex structures such as the shielded gate FET, additional factors such as shield electrode recess and the thickness of the inter-electrode dielectric (i.e., the dielectric layer that insulates the shield and gate electrodes from one another) can cause even larger variations. This high variation takes the form of a higher maximum rating on a data sheet and limits the product's marketability.
Thus, there is a need for techniques which provide a tighter control in the alignment of the body region to the bottom of the gate electrode in trench FETs.